Hydrofluoroether as a heat-transfer fluid

ABSTRACT

The present invention comprises a compound represented by the following structure: 
 
R f —O—R h —O—R f ′
wherein: O is oxygen;  
     R f  and R f′  are, independently, a perfluoroaliphatic group; and  
     R h  is independently a linear, branched or cyclic alkylene group having from  2  to about  8  carbon atoms and at least  4  hydrogen atoms, and  
     wherein the hydrofluoroether compound is free of —O—CH 2 —O—. Another embodiment is an apparatus comprising a device and a mechanism for heat transfer comprising a hydrofluoroether heat-transfer fluid. Another embodiment of the present invention is a method for heat transfer.

FIELD OF INVENTION

This invention relates to hydrofluoroether heat-transfer fluids.

BACKGROUND

Presently various fluids are used for heat transfer. The suitability ofthe heat-transfer fluid depends upon the application process. Forexample, some electronic applications require a heat-transfer fluidwhich is inert, has a high dielectric strength, has low toxicity, goodenvironmental properties, and good heat transfer properties over a widetemperature range. Other applications require precise temperaturecontrol and thus the heat-transfer fluid is required to be a singlephase over the entire process temperature range and the heat-transferfluid properties are required to be predictable, i.e., the compositionremains relatively constant so that the viscosity, boiling point, etc.can be predicted so that a precise temperature can be maintained and sothat the equipment can be appropriately designed.

In the semiconductor industry, there are numerous devices or processesthat require a heat-transfer fluid having select properties. Theheat-transfer fluid may be used to remove heat, add heat, or maintain atemperature.

Each of the semiconductor processes described below incorporates adevice or a work-piece which has heat removed from it or has heat addedto it. The heat transfer associated with either the heat removal oraddition can take place over a wide temperature range. Thus, in eachcase a heat-transfer fluid is preferably used which has other attributesthat make it “operator friendly”. In order for a heat-transfer fluid tobe considered “operator friendly”, the heat-transfer fluid preferablyexhibits low toxicity and low flammability.

For automated test equipment (ATE), equipment is used to test theperformance of semiconductor dice. The dice are the individual “chips”that are cut from a wafer of semiconductor substrate. The dice come fromthe semiconductor foundry and must be checked to ensure they meetfunctionality requirements and processor speed requirements. The test isused to sort “known good dice” (KGD) from dice that do not meet theperformance requirements. This testing is generally performed attemperatures ranging from about −80° C. to about 100° C.

In some cases the dice are tested one-by-one, and an individual die isheld in a chuck. This chuck provides, as part of its design, provisionfor cooling the die. In other cases, several dice are held in the chuckand are tested either sequentially or in parallel. In this situation,the chuck provides cooling for several dice during the test procedure.

It may also be advantageous to test dice at elevated temperatures todetermine their performance characteristics under conditions of elevatedtemperature. In this case, a coolant which has good heat-transferproperties well above room temperature is advantageous.

In some cases, the dice are tested at very low temperatures. Forexample, Complementary Metal-Oxide Semiconductor (“CMOS”) devices inparticular operate more quickly at lower temperatures.

If a piece of ATE equipment employs CMOS devices “on board” as part ofits permanent logic hardware, it may be advantageous to maintain thelogic hardware at a low temperature.

Therefore, to provide maximum versatility to the ATE, a heat-transferfluid preferably performs well at both low and high temperatures (i.e.,preferably has good heat transfer properties over a wide temperaturerange), is inert (i.e., is non-flammable, low in toxicity,non-chemically reactive), has high dielectric strength, has a lowenvironmental impact, and has predictable heat-transfer properties overthe entire operating temperature range.

Etchers operate over temperatures ranging from about 70° C. to about150° C. In this process, reactive plasma is used to anisotropically etchthe features in a wafer. The wafers to be processed are kept at aconstant temperature at each selected temperature. Therefore, theheat-transfer fluid preferably is a single phase over the entiretemperature range. Additionally, the heat-transfer fluid preferably haspredictable performance over the entire range so that the temperaturecan be precisely maintained.

Ashers operate over temperatures ranging from about 40° C. to about 150°C. This is a process that removes the photosensitive organic “mask”.

Steppers operate over temperatures ranging from about 40° C. to about80° C. This is the process step in semiconductor manufacturing where thereticules needed for manufacturing are produced. Reticules are used toproduce the patterns of light and shadow needed to expose thephotosensitive mask. The film used in the steppers is typicallymaintained within a temperature window of +/−0.2° C. to maintain goodperformance of the finished reticule.

PECVD (plasma enhanced chemical vapor deposition) chambers operate overtemperatures ranging from about 50° C. to about 150° C. In this process,films of silicon oxide, silicon nitride, and silicon carbide are grownon a wafer by the chemical reaction initiated in a reagent gas mixturecontaining silicon and either: 1) oxygen; 2) nitrogen; or 3) carbon. Thechuck on which the wafer rests is kept at a uniform, constanttemperature at each selected temperature.

Heat-transfer fluids which are presently used in these semiconductorapplications include perfluorocarbons (PFCs), perfluoropolyethers(PFPEs), perfluoroamines (PFAs), perfluoroethers (PFEs), water/glycolmixtures, deionized water, silicone oils and hydrocarbon oils. However,each of these heat-transfer fluids has some disadvantage. PFCs, PFPEs,PFAs and PFEs may exhibit atmospheric lifetime values of greater than500 years, and up to 5,000 years. Additionally, these materials mayexhibit high global warming potentials (“GWP”). GWP is the integratedpotential warming due to the release of one (1) kilogram of samplecompound relative to the warming due to one (1) kilogram of CO₂ over aspecified integration time horizon. Water/glycol mixtures aretemperature limited, that is, a typical low temperature limit of suchmixtures is −40° C. At low temperatures water/glycol mixtures alsoexhibit relatively high viscosity. The high viscosity at low temperatureyields high pumping power. Deionized water has a low temperature limitof 0° C. Silicone oils and hydrocarbon oils are typically flammable.

Removing heat from electronic devices has become one of the mostimportant obstacles to further improving processor performance. As thesedevices become more powerful, the amount of heat generated per unit timeincreases. Therefore, the mechanism of heat transfer plays an importantrole in processor performance. The heat-transfer fluid preferably hasgood heat transfer performance, good electrical compatibility (even ifused in “indirect contact” applications such as those employing coldplates), as well as low toxicity, low (or non-) flammability and lowenvironmental impact. Good electrical compatibility requires theheat-transfer fluid candidate to exhibit high dielectric strength, highvolume resistivity, and poor solvency for polar materials. Additionally,the heat-transfer fluid candidate must exhibit good mechanicalcompatibility, that is, it must not affect typical materials ofconstruction in an adverse manner. In this application, heat-transferfluid candidates are disqualified if their physical properties are notstable over time.

Materials currently used as heat-transfer fluids for cooling electronicsor electrical equipment include PFCs, PFPEs, silicone oils, andhydrocarbon oils. Each of these heat-transfer fluids has somedisadvantage. PFCs and PFPEs may be environmentally persistent. Siliconeoils and hydrocarbon oils are typically flammable.

Thermal shock testing is generally performed at temperatures rangingfrom about −65° C. to about 150° C. The rapid cycling of temperature ina part or device may be required to simulate the thermal changes broughton by, for instance, launching a missile. Thermal shock testing isrequired for electronics used for military missiles, among other things.There are several military specifications related to thermal shocktesting of many electronic components and assemblies. This test usesvarious means of imparting rapidly changing temperatures within a partor electronic device. One such device employs a liquid heat-transferfluid or liquid heat-transfer fluids that are kept in separatereservoirs maintained at temperature extremes where parts arealternately immersed to induce thermal shock to the test part.Typically, operators load and unload the components or assemblies to andfrom the thermal shock equipment. Therefore, it is important that aheat-transfer fluid used in such an application exhibit low toxicity,low flammability, and low environmental impact. Heat-transfer fluidswhich are liquid over a wide temperature range coupled with lowtoxicity, low flammability, and low environmental impact are ideal forthermal shock testing.

Materials currently used as heat-transfer fluids for liquid/liquidthermal shock test baths include liquid nitrogen, PFCs, and PFPEs. Eachof these heat-transfer fluids has some disadvantage. Liquid nitrogensystems offer limited temperature selectivity at the low temperatureend. PFCs and PFPEs may be environmentally persistent.

Constant temperature baths are typically operated over a broadtemperature range. Therefore, desirable heat-transfer fluids preferablyhave a wide liquid range and good low-temperature heat transfercharacteristics. A heat-transfer fluid having such properties allows avery wide operating range for the constant temperature bath. Typically,most testing fluids require fluid change-out for wide temperatureextremes. Also, good temperature control is essential for accuratelypredicting physical properties of the heat-transfer fluids.

Heat-transfer fluids which are presently used in this applicationinclude: PFCs, perfluoropolyethers (PFPEs), water/glycol mixtures,deionized water, silicone oils, hydrocarbon oils, and hydrocarbonalcohols. Each of these heat-transfer fluids has some disadvantage. PFCsand PFPEs may be environmentally persistent. Water/glycol mixtures aretemperature limited, that is, a typical low temperature limit of suchmixtures is −40° C. At low temperatures water/glycol mixtures alsoexhibit relatively high viscosity. Deionized water has a low temperaturelimit of 0° C. Silicone oils, hydrocarbon oils and hydrocarbon alcoholsare typically flammable.

For heat-transfer processing requiring an inert fluid, fluorinatedmaterials are often used. Fluorinated materials typically have lowtoxicity, are essentially non-irritating to the skin, are non-chemicallyreactive, are non-flammable, and have high dielectric strength.Fluorinated materials such as perfluorocarbons, perfluoropolyethers, andhydrofluoroethers provide the additional advantage of not depleting theozone layer in the stratosphere.

As discussed above, perfluorocarbons, perfluoropolyethers, and somehydrofluoroethers have been used for heat-transfer.

Perfluorocarbons (PFCs) exhibit several traits advantageous to theapplications discussed above. PFCs have high dielectric strength andhigh volume resistivity. PFCs are non-flammable and are generallymechanically compatible with materials of construction, exhibitinglimited solvency. Additionally, PFCs generally exhibit low toxicity andgood operator friendliness. PFCs are manufactured in such a way as toyield a product that has a narrow molecular weight distribution. They doexhibit one important disadvantage, however, and that is longenvironmental persistence.

Perfluoropolyethers (PFPEs) exhibit many of the same advantageousattributes described for PFCs. They also have the same majordisadvantage, i.e., long environmental persistence. In addition, themethods developed for manufacturing these materials yield products thatare not of consistent molecular weight and thus are subject toperformance variability.

Hydrofluoropolyethers (HFPEs), a class of hydrofluoroethers (HFEs),exhibit some of the same advantageous attributes of PFCs, but differgreatly in two areas. To their credit, they exhibit markedly lowerenvironmental persistence, yielding atmospheric lifetimes on the orderof decades rather than millennia. However, some of the HFPEs taught asheat-transfer fluids are a mixture of components of widely disparatemolecular weight. Thus, their physical properties may change over timewhich makes it difficult to predict performance.

Some hydrofluoroethers have been disclosed as heat-transfer fluids.However, the need exists for a heat-transfer fluid which is inert, hashigh dielectric strength, low electrical conductivity, chemicalinertness, thermal stability and effective heat transfer, is liquid overa wide temperature range, has good heat-transfer properties over a widerange of temperatures and also has a shorter atmospheric lifetime, andtherefore a lower global warming potential, than existing heat-transferfluids.

SUMMARY

In one aspect, the present invention comprises a compound which isinert, has high dielectric strength, low electrical conductivity,chemical inertness, thermal stability and effective heat transfer.Additionally, in another embodiment, the present invention comprises acompound that is liquid over a wide temperature range, and has goodheat-transfer properties over a wide range of temperature. The compoundhas the general structure:R_(f)—O—R_(h)—O—R_(f)′

-   -   wherein:    -   O is oxygen;    -   R_(f) and R_(f)′ are, independently, a perfluoroaliphatic group,        and if R_(f) and R_(f)′ contain branched alkylene groups, then        the number of carbons is at least 4;    -   R_(h) is independently a linear, branched or cyclic alkylene        group having from 2 to about 8 carbon atoms and at least 4        hydrogen atoms, and    -   wherein the hydrofluoroether compound is free of formal linkage        (—O—CH₂—O—).

In another aspect, the present invention additionally comprises anapparatus requiring heat-transfer comprising a device, and a mechanismfor transferring heat to or from the device comprising a heat-transferfluid, wherein the heat transfer fluid is represented by the followingstructure:R_(f)—O—R_(h)—O—R_(f)′

-   -   wherein:    -   O is oxygen;    -   R_(f) and R_(f)′ are, independently, a perfluoroaliphatic group;        and    -   R_(h) is independently a linear, branched or cyclic alkylene        group having from 2 to about 8 carbon atoms and at least 4        hydrogen atoms, and    -   wherein the hydrofluoroether compound is free of —O—CH₂—O—.

Another embodiment of the present invention is a method for transferringheat comprising the steps of: providing a device, providing a mechanismfor transferring heat comprising a heat-transfer fluid, and using theheat-transfer fluid to transfer heat to or from the device, wherein theheat-transfer fluid is represented by the following structure:R_(f)—O—R_(h)—O—R_(f)′

-   -   wherein:    -   O is oxygen;    -   R_(f) and R_(f)′ are, independently, a perfluoroaliphatic group;        and    -   R_(h) is independently a linear, branched or cyclic alkylene        group having from 2 to about 8 carbon atoms and at least 4        hydrogen atoms, and    -   wherein the hydrofluoroether compound is free of —O—CH₂—O—.

DETAILED DESCRIPTION

The present invention provides a hydrofluoroether compound, as well asan apparatus and a method for heat-transfer using the hydrofluoroethercompound as a heat-transfer fluid. The apparatus of the presentinvention comprises a device and a mechanism for transferring heatcomprising a heat-transfer fluid.

Perfluorinated means, for the purpose of the present application, thatall the hydrogens in a compound have been replaced with fluorine.

Inert means, for the purpose of the present application, generally notchemically reactive under normal conditions of use.

Formal linkage means —O—CH₂—O—.

Hydrofluoroether Compound

The present application describes a hydrofluoroether compound and theuse of the hydrofluoroether compound as a heat-transfer fluid. Thehydrofluoroether compound may be used to heat, cool, and/or maintain thetemperature of the device at a select temperature. The hydrofluoroethercompound is inert, non-flammable, and environmentally acceptable.Additionally, the hydrofluoroether compound of the present inventionexhibits low viscosity throughout the liquid range, and has good heattransfer properties over a wide temperature range.

The hydrofluoroether compound of the present invention is represented bythe following structure:R_(f)—O—R_(h)—O—R_(f)′

-   -   wherein:    -   O is oxygen;    -   R_(f) and R_(f)′ are, independently, a perfluoroaliphatic group.        R_(f) and R_(f)′ are stable, inert, non-polar, preferably        saturated, monovalent moieties which are both oleophobic and        hydrophobic. R_(f) and R_(f)′ generally contain at least about 2        carbon atoms, for example about 3 to about 20 carbon atoms, and        in specific embodiments from about 3 to about 7 carbon atoms.        R_(f) and R_(f)′ can contain straight chain, branched chain, or        cyclic fluorinated alkylene groups or combinations thereof with        straight chain, branched chain, or cyclic alkylene groups.        Generally, if R_(f) and R_(f)′ contain branched alkylene groups,        then the number of carbons is at least 4. R_(f) and R_(f)′ are        generally free of polymerizable olefinic unsaturation and can        optionally contain catenated heteroatoms such as divalent        oxygen, or trivalent nitrogen. The R_(f) and R_(f)′ groups may        contain at least 5 fluorine atoms, for example at least 7        fluorine atoms, and in some embodiments at least 9 fluorine        atoms (e.g., CF₃CF₂—, CF₃CF₂CF₂CF₂—, (CF₃)₂CFCF₂—, CF₃CF₂CF₂—,        or the like). Perfluorinated aliphatic groups (i.e., those of        the formula C_(x)F_(2x+1), where x is about 2 to about 8, for        example 3 or 4) are examples of embodiments of R_(f) and R_(f)′.

R_(h) is independently a linear, branched or cyclic alkylene grouphaving from 2 to about 8 carbon atoms and at least 4 hydrogen atoms,wherein R_(h) can contain one or more catenated heteroatoms. Examples ofR_(h) include alkylenes, fluoroalkylenes, and the like.

Wherein the hydrofluoroether compound is free of —O—CH₂—O—.

The hydrofluoroether compounds of the present invention are generallyinert. Additionally, the compounds of the present invention may havehigh dielectric strength and low electrical conductivity. The compoundsadditionally are generally thermally stable.

The hydrofluoroether compounds of the present invention are useful asheat transfer liquids. The compounds generally exhibit a liquid phaseover a wide temperature range. For example, the compounds are generallyliquid to at least about −50° C. Generally, the viscosity of thecompounds in the liquid phase is less than 100 centistokes at −50° C.(100×10⁻⁶ m²/s), preferably less than 50 centistokes (50×10⁻⁶ m²/s) .

The hydrofluoroether compounds of the present invention additionallyhave low global warming potential values (GWP), in some embodimentsunder 500. GWP is determined using a calculated value for atmosphericlifetime and an experimentally determined infrared absorbance dataintegrated over the spectral region of interest, typically 500 to 2500cm⁻¹. A detailed description of GWP can be found, for example in U.S.Pat. No. 5,925,611, which is incorporated by reference.

The hydrofluoroether compounds of the present invention are generallyprepared by alkylation of perfluorinated acyl fluorides withpolyfunctional alkylating agents, for example dimesylates andditosylates using fluoride ion in a polar aprotic solvent.

Apparatus

In certain embodiments, the invention includes an apparatus requiringheat transfer. The apparatus comprises a device and a mechanism fortransferring heat to or from the device using a heat-transfer fluid.Such apparatus include refrigeration systems, cooling systems, testingequipment, and machining equipment.

Examples of an apparatus of the present invention include, but are notlimited to, test heads used in automated test equipment for testing theperformance of semiconductor dice; wafer chucks used to hold siliconwafers in ashers, steppers, etchers, PECVD tools; constant temperaturebaths, and thermal shock test baths.

Device

In certain embodiments, the present invention comprises a device. Thedevice is defined herein as a component, work-piece, assembly, etc. tobe cooled, heated or maintained at a selected temperature. Such devicesinclude electrical components, mechanical components and opticalcomponents. Examples of devices of the present invention include, butare not limited to microprocessors, wafers used to manufacturesemiconductor devices, power control semiconductors, electricaldistribution switch gear, power transformers, circuit boards, multi-chipmodules, packaged and unpackaged semiconductor devices, chemicalreactors, nuclear reactors, fuel cells, lasers, and missile components.

Heat Transfer Mechanism

In certain embodiments, the present invention comprises a mechanism fortransferring heat. Heat is transferred by placing the heat transfermechanism in thermal contact with the device. The heat transfermechanism, when placed in thermal contact with the device, removes heatfrom the device or provides heat to the device, or maintains the deviceat a selected temperature. The direction of heat flow (from device or todevice) is determined by the relative temperature difference between thedevice and the heat transfer mechanism.

The heat transfer mechanism comprises the heat-transfer fluid of thepresent invention.

Additionally, the heat transfer mechanism may include facilities formanaging the heat-transfer fluid, including, but not limited to: pumps,valves, fluid containment systems, pressure control systems, condensers,heat exchangers, heat sources, heat sinks, refrigeration systems, activetemperature control systems, and passive temperature control systems.

Examples of suitable heat transfer mechanisms include, but are notlimited to, temperature controlled wafer chucks in PECVD tools,temperature controlled test heads for die performance testing,temperature controlled work zones within semiconductor processequipment, thermal shock test bath liquid reservoirs, and constanttemperature baths.

In some systems, such as etchers, ashers, PECVD chambers, thermal shocktesters, the upper desired operating temperature may be as high as 150°C.

Method

The present invention additionally comprises a method for transferringheat comprising the steps of: providing a device, providing a mechanismfor transferring heat comprising a heat-transfer fluid, and using theheat-transfer fluid to transfer heat to or from the device, wherein theheat-transfer fluid is represented by the following structure:R_(f)—O—R_(h)—O—R_(f)′.

EXAMPLES

The present invention will be further described with reference to thefollowing nonlimiting examples and test methods. All parts, percentages,and ratios are by weight unless otherwise specified.

Example 11,1,1,2,2,3,3-Heptafluoro-3-(3-heptafluoropropyloxy-propoxy)-propane(CF₃CF₂CF₂OCH₂CH₂CH₂OCF₂CF₂CF₃)

Into a clean dry 600 mL Parr reactor equipped with stirrer, heater andthermocouple were added 20.1 g (0.35 mole) of anhydrous potassiumfluoride, 49.8 g (0.13 mole) of 1,3-propanediol di-p-tosylate (TCIAmerica), 4.4 grams of Adogen™ 464 (Aldrich) and 300 ml. of anhydrousdiglyme (anhydrous diethylene glycol dimethyl ether, available fromSigma Aldrich Chemical Co. used in all subsequent syntheses). Theanhydrous potassium fluoride used in this synthesis, and in allsubsequent syntheses, was spray dried, stored at 125° C. and groundshortly before use. The reactor was sealed and cooled to about −50° C.and a vacuum pump used to evacuate the vapor space. 53.5 g (0.30 mole)of C₂F₅C(O)F (approximately 95.0 percent purity) was added to the sealedreactor. The reactor and its contents were then heated to 75° C. andheld for 21 hours. Pressure decreased from 86 psig to 12.1 psig duringthe reaction. The reactor contents were allowed to cool and excesspressure was vented. The reactor contents were added to a 500 ml. roundbottom flask equipped with a mechanical stirrer, temperature probe,water condenser and Dean-Stark receiver. Deionized water (200 ml) wasadded to the flask and the mixture steam distilled to give 49.0 grams oflower phase distillate containing 65.8% of C₃F₇OC₃H₆OC₃F₇ as determinedby gas-chromatography. The crude product was azeotropically distilledfrom 100 g of 22.5% aqueous potassium hydroxide. The product was waterwashed, dried with anhydrous sodium sulfate and fractionally distilledto provide 8.2 g of 97.3% purity1,1,1,2,2,3,3-heptafluoro-3-(3-heptafluoropropyloxy-propoxy)-propane.The boiling point was 159° C. and the structure was confirmed by gaschromatography-mass spectrometry (gc-ms). The viscosity was 9centistokes (9×10⁻⁶ m²/s) at −50° C. measured using a Cannon-Fenskeviscometer and a Wescan Model 221 viscosity timer.

Example 21,1,1,2,2,3,3,4,4-Nonafluoro-4-(3-nonafluorobutyloxy-propoxy)-butane(CF₃CF₂CF₂CF₂OCH₂CH₂CH₂OCF₂CF₂CF₂CF₃)

This compound was prepared by the method of Example 1 using 24.0 g (0.41mole) potassium fluoride, 75.0 g 1,3-propanediol di-p-tosylate(Alfa-Aesar), 4.7 g. Adogen™ 464 and 200 ml of diglyme, and 75.0 gCF₃CF₂CF₂C(O)F (approximately 95% purity). The reactor contents wereheated to 75° C. and held 120 hours. The final pressure was 8.0 psig.The reactor was vented and the contents added to 1-liter round bottomflask. 200 grams of 22.5% KOH was added to the flask and the contentssteam distilled and then water washed to provide 52.8 g of materialcontaining 64.5% of CF₃CF₂CF₂CF₂OC₃H₆OCF₂CF₂CF₂CF₃ as determined by gaschromatography. The crude product was fractionally distilled to provide19.3 g of 100% pure1,1,1,2,2,3,3,4,4-nonafluoro-4-(3-nonafluorobutyloxy-propoxy)-butane.The boiling point was 190° C. and the structure was confirmed by gc-ms.The viscosity was 25 centistokes (25×10⁻⁶ m²/s) at −50° C. measuredusing a Cannon-Fenske viscometer and a Wescan Model 221 viscosity timer.

Example 31,1,1,2,2,3,3-Heptafluoro-3-(2-heptafluoropropyloxy-ethoxy)-propane(CF₃CF₂CF₂OCH₂CH₂OCF₂CF₂CF₃)

This compound was prepared by the method of Example 1 using 19.4 g (0.33mole) potassium fluoride, 48.9 g (0.13 mole) of 1,2-ethylene glycoldi-p-tosylate (Aldrich), 4.7 g of Adogen™ 464 and 302.7 g of diglyme and47.0 grams of CF₃CF₂CF₂C(O)F (approximately 95% purity). The reactor washeld at 50° C. for 40 hours. The reactor was vented and the contentswere added to a 3-liter round bottom flask equipped with a mechanicalstirrer, temperature probe, water condenser and Dean-Stark receiver. Thecontents of another reaction run similarly were also added to the3-Liter flask. 150 grams of 22.5% KOH was added to the flask and themixture steam distilled and then water washed to give 41.1 grams ofmaterial containing 90.2% of CF₃CF₂CF₂OC₂H₄OCF₂CF₂CF₃ as determined bygas chromatography. The crude product was fractionally distilled toprovide 21.6 grams of 99.4% purity of1,1,1,2,2,3,3-heptafluoro-3-(2-heptafluoropropyloxy-ethoxy)-propane. Theboiling point was 145° C. and the structure was confirmed by gc-ms. Theviscosity was 7 centistokes (7×10⁻⁶ m²/s) at −50° C. measured using aCannon-Fenske viscometer and a Wescan Model 221 viscosity timer.

Example 41,1,1,2,2,3,3,4,4,5,5-Undecafluoro-5-(3-undecafluoropentyloxy-propoxy)-pentane(CF₃CF₂CF₂CF₂CF₂OCH₂CH₂CH₂OCF₂CF₂CF₂CF₂CF₃)

This compound was prepared by the method of Example 1 using 19.3 g (0.33mole) potassium fluoride, 50.5 g (0.13 mole) of 1,3-propanedioldi-p-tosylate (Alfa Aesar), 3.8 g of Adogen™ 464 and 251.4 g of diglymeand 69 grams of CF₃CF₂CF₂CF₂C(O)F (approximately 95% purity). Thereactor was held at 90° C. for 24 hours. Final reactor pressure was 1.5psig. The reactor contents were added to a 2-liter round bottom flaskequipped with a mechanical stirrer, temperature probe, water condenserand Dean-Stark receiver. 120 grams of 22.5% KOH was added to the flaskand the mixture steam distilled and then water washed to give 46.9 gramsof material containing 74.1% of CF₃CF₂CF₂CF₂CF₂OC₃H₆OCF₂CF₂CF₂CF₂CF₃ asdetermined by gas chromatography. The crude product was fractionallydistilled to provide 23.2 grams of 98.2% pure1,1,1,2,2,3,3,4,4,5,5-undecafluoro-5-(3-undecafluoropentyloxy-propoxy)-pentane.The boiling point was 208.1° C. and the structure was confirmed bygc-ms. The viscosity was 85 centistokes (85×10⁻⁶ m²/s) at −50° C.measured using a Cannon-Fenske viscometer and a Wescan Model 221viscosity timer.

Example 51,1,1,2,2,3,4,5,5,5-Decafluoro-3-{3-[1,2,2,3,3,3-hexafluoro-1-(1,2,2,2-tetrafluoro-1-trifluoromethyl-ethyl)-propoxy]-propoxy}-4-trifluoromethyl-pentane(CF₃CF₂CF[CF(CF₃)₂]OCH₂CH₂CH₂OCF[CF(CF₃)₂]CF₂CF₃)

This compound was prepared by the method of Example 1 using 8.4 g (0.14mole) potassium fluoride, 25.0 g (0.06 mole) of 1,3-propanedioldi-p-tosylate (Alfa Aesar), 1.5 g of Adogen™ 464 and 150 ml of diglymeand 34.3 grams of CF₃CF₂C(O)CF(CF₃)₂ (approximately 99% purity). Reactorwas held at 100° C. for 22 hours. Final reactor pressure was 8.1 psig.The reactor contents were added to a round bottom flask equipped with amechanical stirrer, temperature probe, water condenser and Dean-Starkreceiver. 40 grams of 37.5% KOH was added to the flask and the mixturesteam distilled and then water washed to give 19.3 grams of materialcontaining 47.3% of CF₃CF₂CF[CF(CF₃)₂]OCH₂CH₂CH₂OCF[CF(CF₃)₂]CF₂CF₃ asdetermined by gas chromatography. The structure was confirmed by gc-ms.

Example 61,1,1,2,2,3,3,4,4-Nonafluoro-4-(4-nonafluorobutyloxy-butoxy)butane(CF₃CF₂CF₂CF₂OCH₂CH₂CH₂CH₂OCF₂CF₂CF₂CF₃)

In a manner similar to that described in Example 1, potassium fluoride(20.7 g, 0.356 mole), 1,4-butanediol dimethanesulfonate (40 g, 0.162mole, Aldrich), Adogen™ 464 (8.8 g of a 55% solution in anhydrousdiglyme) and anhydrous diglyme (300 ml) were combined in a 600 mL Parrreactor. After the reactor had been cooled and evacuated as describedabove, n-C₃F₇COF (84.2 g of 95% purity, 0.37 mole) was added and thereactor then heated to 75° C. for 19 hours. The temperature was thenraised to 80° C. for an additional 20 hours. Pressure decreased from 72psig to 25 psig during the reaction. The reactor contents were allowedto cool and excess pressure was vented. The reactor contents weretransferred to a 1 L round bottom flask with about 300 mL of water. Themixture was azeotropically distilled as described in Example 1 to obtain48 g of a lower fluorochemical phase after phase separation and washingwhich contained 66% of the desired C₄F₉OC₄H₈OC₄F₉ product. The crudeproduct was azeotropically distilled from about 100 g of 45% potassiumhydroxide using the same apparatus as for the first distillation and thelower fluorochemical phase water washed and fractionally distilled toprovide 18.3 g of 99.5% purity1,1,1,2,2,3,3,4,4-nonafluoro-4-(4-nonafluorobutyloxy-butoxy)butane. Theboiling point was 208° C. and the structure was confirmed by gc-ms. Theviscosity was 41 centistokes (41×10⁻⁶ m²/s) at −50° C. measured using aCannon-Fenske viscometer and a Wescan Model 221 viscosity timer.

Example 7 n,i-C₄F₉OC₃H₆On,i-C₄F₉ (This product is an inseparable mixtureof n-C₄F₉ and iso-C₄F₉ groups on either end of the molecule)

In a manner similar to that described in Example 1, potassium fluoride(17.4 g, 0.3 mole), 1,3-propanediol di-p-tosylate (55 g, 0.143 mole,Aldrich), Adogen™ 464 (8.3 g of a 55% solution in anhydrous diglyme) andanhydrous diglyme (271 g) were combined in a 600 mL Parr reactor. Afterthe reactor had been cooled and evacuated as described above, a mixtureof n-C₃F₇COF and i-C₃F₇COF (100 g of 70% purity, 0.324 mole, about 60%iso and 40% normal) was added and the reactor then heated to 75° C. forabout 64 hours. Pressure decreased from 115 psig to 65 psig during thereaction. The reactor contents were allowed to cool and excess pressurewas vented. The reactor contents were transferred to a 1 L round bottomflask with about 300 mL of water. The mixture was azeotropicallydistilled as described in Example 1 to obtain 58.4 g of a lowerfluorochemical phase after phase separation and washing which contained85% of the desired C₄F₉OC₃H₆OC₄F₉ product. The crude product was againazeotropically distilled from about 100 g of 45% potassium hydroxide.The lower fluorochemical phase was water washed and fractionallydistilled to provide 32.2 g of 95.5% purity product. The boiling rangewas 188-190° C. and the structure was confirmed by gc-ms. The viscositywas 35 centistokes (35×10⁻⁶ m²/s) at −50° C. measured using aCannon-Fenske viscometer and a Wescan Model 221 viscosity timer.

Example 8 n,i-C₄F₉OC₄H₈On,i-C₄F₉ (This product is an inseparable mixtureof n-C₄F₉ and iso-C₄F₉ groups on either end of the molecule)

In a manner similar to that described in Example 1, potassium fluoride(17.1 g, 0.29 mole), 1,4-butanediol dimethanesulfonate (30.1 g, 0.12mole, Aldrich), Adogen™ 464 (4.5 g of a 55% solution in anhydrousdiglyme) and anhydrous diglyme (278 g) were combined in a 600 mL Parrreactor. After the reactor had been cooled and evacuated as describedabove, a mixture of n-C₃F₇COF and i-C₃F₇COF (73.6 g of 70% purity, 0.24mole, about 60% iso and 40% normal) was added and the reactor thenheated to 75° C. for about 64 hours. Pressure decreased from 100 psig to50 psig during the reaction. The reactor contents were allowed to cooland excess pressure was vented. The reactor contents were transferred toa 1 L round bottom flask with about 300 mL of water. The mixture wasazeotropically distilled as described in Example 1 to obtain 28 g of alower fluorochemical phase after phase separation and washing whichcontained 60% of the desired C₄F₉OC₄H₈OC₄F₉ product. The crude productwas again azeotropically distilled from about 100 g of 45% potassiumhydroxide. After separation and water washing of the lower phase, thissample was combined with another sample prepared in essentially the samemanner and the combined sample was fractionally distilled to provide19.2 g of 90.7% purity product. The boiling range was 206-208° C. andthe structure was confirmed by gc-ms. The viscosity was 51 centistokes(51×10⁻⁶ m²/s) at −50° C. measured using a Cannon-Fenske viscometer anda Wescan Model 221 viscosity timer.

Example 91,1,1,2,2,3,3,4,4-Nonafluoro-4-(2-nonafluorobutyloxy-ethoxy)butane(CF₃CF₂CF₂CF₂OCH₂CH₂OCF₂CF₂CF₂CF₃)

In a manner similar to that described in Example 1, potassium fluoride(18.8 g, 0.32 mole), 1,2-ethanediol di-p-tosylate (50 g, 0.135 mole,Aldrich), Adogen™ 464 (5.5 g of a 55% solution in anhydrous diglyme) andanhydrous diglyme (278 g) were combined in a 600 mL Parr reactor. Afterthe reactor had been cooled and evacuated as described above, n-C₃F₇COF(61.4 g of 95% purity, 0.27 mole) was added and the reactor then heatedto 75° C. for about 30 hours. Pressure decreased from 65 psig to −11.9psig during the reaction. Since the reactor was initially evacuated, thefinal pressure assuming complete reaction and no unreactive volatilematerials remaining would be negative as measured by the pressuretransducer. The reactor contents were allowed to cool to ambienttemperature and the reactor opened. The reactor contents weretransferred to a 1 L round bottom flask with about 300 mL of water. Themixture was azeotropically distilled as described in Example 1 to obtain29 g of a lower fluorochemical phase after phase separation and washingwhich contained 42% of the desired C₄F₉OC₂H₄OC₄F₉ product. In this case,the product was first distilled using a concentric tube column and adistillation cut from 175-182° C. was subsequently treated with 45%potassium hydroxide in the usual manner. The purity at this stage wasnow 95.9% of the desired diether as confirmed by gc-ms.

Example 101,1,1,2,2,3,3,4,4-Nonafluoro-4-(2-(2-nonafluorobutyloxy-ethoxy-ethoxy)butane(CF₃CF₂CF₂CF₂OCH₂CH₂OCH₂CH₂OCF₂CF₂CF₂CF₃)

In a manner similar to that described in Example 1, potassium fluoride(16.8 g, 0.29 mole) diethylene glycol di-p-tosylate (50 g, 0.121 mole,Aldrich), Adogen™ 464 (6.2 g of a 55% solution in anhydrous diglyme) andanhydrous diglyme (278 g) were combined in a 600 mL Parr reactor. Afterthe reactor had been cooled and evacuated as described above, n-C₃F₇COF(53.5 g of 95% purity, 0.24 mole) was added and the reactor then heatedto 75° C. for about 17 hours. Pressure decreased from 47 psig to −1.6psig during the reaction. The reactor contents were allowed to cool toambient temperature and the reactor opened. The reactor contents weretransferred to a 1 L round bottom flask with about 300 mL of water. Themixture was azeotropically distilled as described in Example 1 to obtain46 g of a lower fluorochemical phase after phase separation and washingwhich contained 75% of the desired C₄F₉OC₂H₄OC₂H₄OC₄F₉ product. Thismaterial was not subsequently treated with KOH and was found to be 90%desired product having a distillation range of 218-219° C. The viscositywas 64 centistokes (64×10⁻⁶ m²/s) at −50° C. measured using aCannon-Fenske viscometer and a Wescan Model 221 viscosity timer.

Example 111,1,2,2,3,3-Hexafluoro-1-[3-(1,1,2,2,3,3-hexafluoro-3-trifluoromethoxy-propoxy)-propoxy]-3-trifluoromethoxy-propane(CF₃OCF₂CF₂CF₂OCH₂CH₂CH₂OCF₂CF₂CF₂OCF₃)

This compound was prepared by the method of Example 1 using 23.9 g (0.41mole) potassium fluoride, 49.5 g (0.13 mole) 1,3-propanedioldi-p-tosylate (Alfa-Aesar), 4.1 g Adogen™ 464 and 300 ml of diglyme, and72.4 g CF₃OCF₂CF₂C(O)F (approximately 95% purity). The reactor contentswere heated to 75° C. and held 89 hours. The reactor was vented and thecontents added to 1-liter round bottom flask. 150 grams of water wereadded to the flask and the contents steam distilled and then waterwashed to provide 58.3 g of material containing 93.6% ofCF₃OCF₂CF₂CF₂OC₃H₆OCF₂CF₂CF₂OCF₃ as determined by gas chromatography.The crude product was fractionally distilled to provide 18.6 g of 97.3%pure1,1,2,2,3,3-Hexafluoro-1-[3-(1,1,2,2,3,3-hexafluoro-3-trifluoromethoxy-propoxy)-propoxy]-3-trifluoromethoxy-propane.The boiling point was 191° C. and the structure was confirmed by gc-ms.The viscosity was 19 centistokes (19×10⁻⁶ m²/s) at −50° C. measuredusing a Cannon-Fenske viscometer and a Wescan Model 221 viscosity timer.

Various modifications and alterations to this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention. It should be understood that thisinvention is not intended to be unduly limited by the illustrativeembodiments and examples set forth herein and that such examples andembodiments are presented by way of example only with the scope of theinvention intended to be limited only by the claims as set forth hereinas follows.

1. A compound represented by the general formula:R_(f)—O—R_(h)—O—R_(f)″wherein: O is oxygen; R_(f) and R_(f)′ are,independently, a perfluoroaliphatic group, and if R_(f) and R_(f)′contain branched alkylene groups, then R_(f) and R_(f)′ contain at least4 carbons; R_(h) is independently a linear, branched or cyclic alkylenegroup having from 2 to about 8 carbon atoms and at least 4 hydrogenatoms, and wherein the hydrofluoroether compound is free of —O—CH₂—O—.2. The compound of claim 1 wherein R_(f) and R_(f)′ contain,independently, at least about 2 carbon atoms.
 3. The compound of claim 2wherein R_(f) and R_(f)′ contain, independently, about 3 to about 20carbon atoms.
 4. The compound of claim 2 wherein R_(f) and R_(f)′contain, independently, 3 to about 7 carbon atoms.
 5. The compound ofclaim 1 wherein R_(f) and R_(f)′ contain at least 5 fluorine atoms. 6.The compound of claim 5 wherein R_(f) and R_(f)′ contain, independently,at least 7 fluorine atoms.
 7. The compound of claim 5 wherein R_(f) andR_(f)′ contain, independently, at least 9 fluorine atoms.
 8. Thecompound of claim 1 wherein R_(f) and R_(f)′ are, independently,C_(x)F_(2x+1), where x is about 2 to about
 8. 9. The compound of claim 8wherein x is 3 or
 4. 10. The compound of claim 1 wherein the compoundhas a viscosity is less than 100 centistokes (100×10⁻⁶ m²/s) at −50° C.11. The compound of claim 10 wherein the compound has a viscosity ofless than 50 centistokes (50×10⁻⁶ m²/s) at −50° C.
 12. An apparatusrequiring heat transfer comprising: (a) a device; and (b) a mechanismfor transferring heat to or from the device, comprising using aheat-transfer fluid, wherein the heat transfer fluid is represented bythe following structure:R_(f)—O—R_(h)—O—R_(f)′ wherein: O is oxygen; R_(f) and R_(f)′ are,independently, a perfluoroaliphatic group; and R_(h) is independently alinear, branched or cyclic alkylene group having from 2 to about 8carbon atoms and at least 4 hydrogen atoms, and wherein thehydrofluoroether compound is free of —O—CH₂—O—.
 13. The apparatusaccording to claim 12, wherein the device is selected from the groupconsisting of microprocessors, wafers used to manufacture semiconductordevices, power control semiconductors, electrical distribution switchgear, power transformers, circuit boards, multi-chip modules, packagedand unpackaged semiconductor devices, chemical reactors, nuclearreactors, fuel cells, lasers, and missile components.
 14. The apparatusaccording to claim 12, wherein the device is heated.
 15. The apparatusaccording to claim 12, wherein the device is cooled.
 16. The apparatusaccording to claim 12, wherein the device is maintained at a selectedtemperature.
 17. The apparatus according to claim 12, wherein themechanism for transferring heat is selected from the group consisting oftemperature controlled wafer chucks in PECVD tools, temperaturecontrolled test heads for die performance testing, temperaturecontrolled work zones within semiconductor process equipment, thermalshock test bath liquid reservoirs, and constant temperature baths
 18. Amethod for transferring heat comprising the steps of: (a) providing adevice; and (b) using a heat-transfer fluid to transfer heat to or fromthe device, wherein the heat-transfer fluid is represented by thefollowing structure:R_(f)—O—R_(h)—O—R_(f)′ wherein: O is oxygen; R_(f) and R_(f)′ are,independently, a perfluoroaliphatic group; and R_(h) is independently alinear, branched or cyclic alkylene group having from 2 to about 8carbon atoms and at least 4 hydrogen atoms, and wherein thehydrofluoroether compound is free of —O—CH₂—O—.